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Register a new userObservation of the $Lambda_b^0toLambdaphi$ decay
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The $Lambda_b^0toLambdaphi$ decay is observed using data corresponding to an integrated luminosity of 3.0fb$^{-1}$ recorded by the LHCb experiment. The decay proceeds at leading order via a $bto sbar{s}s$ loop transition and is therefore sensitive to the possible presence of particles beyond the Standard Model. A first observation is reported with a significance of $5.9$ standard deviations. The value of the branching fraction is measured to be $(5.18pm1.04pm0.35,^{+0.67}_{-0.62})times10^{-6}$, where the first uncertainty is statistical, the second is systematic, and the third is related to external inputs. Triple-product asymmetries are measured to be consistent with zero.
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The Cabibbo-suppressed decay $Lambda_b^0rightarrowchi_{c1}ppi^-$ is observed for the first time using data from proton-proton collisions corresponding to an integrated luminosity of 6fb$^{-1}$, collected with the LHCb detector at a centre-of-mass energy of 13TeV. Evidence for the $Lambda_b^0rightarrowchi_{c2}ppi^-$ decay is also found. Using the $Lambda_b^0rightarrowchi_{c1}pK^-$ decay as normalisation channel, the ratios of branching fractions are measured to be $$begin{array}{rcl} frac{ mathcal{B} (Lambda_b^0rightarrowchi_{c1}ppi^-)}{mathcal{B} (Lambda_b^0rightarrowchi_{c1}pK^-)} & = & (6.59 pm 1.01 pm 0.22 ) times 10^{-2} ,, frac{mathcal{B} (Lambda_b^0rightarrowchi_{c2}ppi^-)}{mathcal{B} (Lambda_b^0rightarrowchi_{c1}ppi^-)} & = & 0.95 pm 0.30 pm 0.04 pm 0.04 ,, frac{mathcal{B} (Lambda_b^0rightarrowchi_{c2}pK^-)}{mathcal{B} (Lambda_b^0rightarrowchi_{c1}pK^-)} & = & 1.06 pm 0.05 pm 0.04 pm 0.04 ,,end{array}$$ where the first uncertainty is statistical, the second is systematic and the third is due to the uncertainties in the branching fractions of $chi_{c1,2}rightarrow J/psigamma$ decays.
Using proton-proton collision data, collected with the LHCb detector and corresponding to 1.0, 2.0 and 1.9fb$^{-1}$ of integrated luminosity at the centre-of-mass energies of 7, 8, and 13 TeV, respectively, the decay $Lambda_b^0to chi_{c1}(3872)pK^-$ with $chi_{c1}to J/psipi^+pi^-$ is observed for the first time. The significance of the observed signal is in excess of seven standard deviations. It is found that $(58pm15)%$ of the decays proceed via the two-body intermediate state $chi_{c1}(3872)Lambda(1520)$. The~branching fraction with respect to that of the $Lambda_brightarrowpsi(2S)p K^{-}$ decay mode, where the $psi(2S)$~meson is reconstructed in the $J/psi pi^+pi^-$ final state, is measured to be: begin{equation*} frac{Lambda_b^0tochi_{c1}(3872)pK^-}{Lambda_btopsi(2S)p K^-} times frac{mathcal{B}(chi_{c1} to J/psi pi^+pi^-)}{mathcal{B}(psi(2S)to J/psi pi^+pi^-)} = left(5.4 pm 1.1 pm 0.2right)times 10^{-2},, end{equation*} where the first uncertainty is statistical and the second is systematic.
The first observation of the Cabibbo-suppressed decay $Lambda_b^0rightarrow J/psi p pi^-$ is reported using a data sample of proton-proton collisions at 7 and 8 TeV, corresponding to an integrated luminosity of 3 $rm fb^{-1}$. A prominent signal is observed and the branching fraction relative to the decay mode $Lambda_b^0rightarrow J/psi p K^-$ is determined to be $$ frac{{cal B}(Lambda_b^0rightarrow J/psi p pi^-)}{{cal B}(Lambda_b^0rightarrow J/psi p K^-)}=0.0824pm0.0025:(text{stat})pm0.0042:(text{syst}). $$ A search for direct CP violation is performed. The difference in the CP asymmetries between these two decays is found to be $$ {cal A}_{CP}(Lambda_b^0rightarrow J/psi p pi^-)-{cal A}_{CP}(Lambda_b^0rightarrow J/psi p K^-)=(+5.7pm 2.4:(text{stat})pm1.2:(text{syst}))%, $$ which is compatible with CP symmetry at the $2.2sigma$ level.
The decay $Lambda_b^0 to Lambda_c^+ p overline{p} pi^-$ is observed using $pp$ collision data collected with the LHCb detector at centre-of-mass energies of $sqrt{s}=$ 7 and 8 TeV, corresponding to an integrated luminosity of 3 $fb^{-1}$. The ratio of branching fractions between $Lambda_b^0 to Lambda_c^+ p overline{p} pi^-$ and $Lambda_b^0 to Lambda_c^+ pi^-$ decays is measured to be begin{equation*} frac{mathcal{B}(Lambda_b^0 to Lambda_c^+ p overline{p}pi^-)}{mathcal{B}(Lambda_b^0 to Lambda_c^+ pi^-)} = 0.0540 pm 0.0023 pm 0.0032. end{equation*} Two resonant structures are observed in the $ Lambda_c^+ pi^-$ mass spectrum of the ${Lambda_b^0 to Lambda_c^+ poverline{p} pi^-}$ decays, corresponding to the $Sigma_c(2455)^0$ and $Sigma_c^{*}(2520)^0$ states. The ratios of branching fractions with respect to the decay $Lambda_b^0 to Lambda_c^+ p overline{p} pi^-$ are begin{align*} frac{mathcal{B}(Lambda_b^0 to Sigma_c^0 poverline{p})timesmathcal{B}(Sigma_c^0to Lambda_c^+ pi^-)}{mathcal{B}(Lambda_b^0 to Lambda_c^+ p overline{p}pi^-)} = 0.089pm0.015pm0.006, frac{mathcal{B}(Lambda_b^0 to Sigma_c^{*0} poverline{p})timesmathcal{B}(Sigma_c^{*0}to Lambda_c^+ pi^-)}{mathcal{B}(Lambda_b^0 to Lambda_c^+ p overline{p}pi^-)} = 0.119pm0.020pm0.014. end{align*} In all of the above results, the first uncertainty is statistical and the second is systematic. The phase space is also examined for the presence of dibaryon resonances. No evidence for such resonances is found.
The decay $Lambda_b^0 to eta_c(1S) p K^-$ is observed for the first time using a data sample of proton-proton collisions, corresponding to an integrated luminosity of 5.5 $fb^{-1}$, collected with the LHCb experiment at a center-of-mass energy of 13 TeV. The branching fraction of the decay is measured, using the $Lambda_b^0 to J/psi p K^-$ decay as a normalization mode, to be $mathcal{B}(Lambda_b^0 to eta_c(1S) p K^-)=(1.06pm0.16pm0.06^{+0.22}_{-0.19})times10^{-4}$, where the quoted uncertainties are statistical, systematic and due to external inputs, respectively. A study of the $eta_c(1S) p$ mass spectrum is performed to search for the $P_c(4312)^+$ pentaquark state. No evidence is observed and an upper limit of begin{equation*} frac{mathcal{B}(Lambda_b^0 to P_c(4312)^+ K^-)times mathcal{B}(P_c(4312)^+ to eta_c(1S) p)}{mathcal{B}(Lambda_b^0 to eta_c(1S) p K^-)} < 0.24 end{equation*} is obtained at the 95% confidence level.
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